1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. Furthermore, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor, a semiconductor device, a display device, a light-emitting device, a lighting device, a power storage device, a memory device, or a processor. The present invention relates to a method for manufacturing a semiconductor, a semiconductor device, a display device, a light-emitting device, a lighting device, a power storage device, a memory device, or a processor. The present invention relates to a method for driving a semiconductor device, a display device, a light-emitting device, a lighting device, a power storage device, a memory device, or a processor.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, a light-emitting device, a lighting device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
A technique for forming a transistor by using a semiconductor over a substrate having an insulating surface has attracted attention. The transistor is applied to a wide range of semiconductor devices such as an integrated circuit and a display device. Silicon is known as a semiconductor applicable to a transistor.
Whether amorphous silicon, polycrystalline silicon, single crystal silicon, or the like is used as a semiconductor in a transistor depends on the purpose. For example, in the case of a transistor included in a large display device, amorphous silicon, which can be formed using an established technique for forming a film over a large-sized substrate, is preferably used. On the other hand, in the case of a transistor included in a high-performance display device where driver circuits are formed over the same substrate, polycrystalline silicon, which can form a transistor having high field-effect mobility, is preferably used. In the case of using a transistor included in an integrated circuit or the like, it is preferable to use single crystal silicon having higher field-effect mobility. As a method for forming polycrystalline silicon, high-temperature heat treatment or laser light treatment which is performed on amorphous silicon has been known.
In recent years, an oxide semiconductor has attracted attention. An oxide semiconductor can be formed by a sputtering method or the like, and thus can be used for a semiconductor of a transistor in a large-sized display device. A transistor including an oxide semiconductor has high field-effect mobility; therefore, a high-performance display device where driver circuits are formed over the same substrate can be obtained. In addition, there is an advantage that capital investment can be reduced because part of production equipment for a transistor including amorphous silicon can be retrofitted and utilized.
As a method for providing a transistor including an oxide semiconductor with stable electrical characteristics, a technique where an insulator in contact with an oxide semiconductor is doped with oxygen is disclosed (see Patent Document 1). The technique disclosed in Patent Document 1 enables oxygen vacancies in an oxide semiconductor to be reduced. As a result, variation in electrical characteristics of a transistor including an oxide semiconductor can be reduced and reliability can be improved.
A transistor including an oxide semiconductor is known to have an extremely low leakage current in an off state. For example, a low-power CPU and the like utilizing the leakage current of a transistor including an oxide semiconductor are disclosed (see Patent Document 2).
Patent Document 3 discloses that a transistor having high field-effect mobility can be obtained by a well potential formed using an active layer formed of a semiconductor.